Aeronautics and astronautics – Spacecraft – Spacecraft formation – orbit – or interplanetary path
Reexamination Certificate
2001-12-10
2004-11-30
Eldred, J. Woodrow (Department: 3644)
Aeronautics and astronautics
Spacecraft
Spacecraft formation, orbit, or interplanetary path
C455S012100, C455S013100, C455S013200, C342S352000, C342S356000
Reexamination Certificate
active
06824107
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates specifically to an artificial satellite, which is usable in the field of communications, such as satellite communications and mobile communications, a satellite orbit control method and a communication system using the satellite.
There is a requirement to transfer medical information including image data, for an emergency case carried on an ambulance from the ambulance to a paramedic center, and to direct medical treatment suitable for the emergency case to the ambulance from the doctors on duty at the paramedic center.
However, in the case of trying to transfer large-sized data, like image files, satisfactory results can not obtained by the conventional ground-base communication infrastructure. In addition, in case of communicating via geostationary satellites currently in service and/or mobile communication satellites to be deployed in the future, it is difficult to establish stable and continuous transfer lines extended from moving bodies because of shielding objects such as building structures and trees.
Though it is certainly possible to transfer large-sized data from movable objects, like an automobile, by using satellites moving in a specific orbit, no definite method for defining such an orbit has been established to date. Therefore, the orbit-related elements of such a specific orbit have not been definitely identified as yet.
Conventional technologies and their problems are described below in detail.
(A) Technologies and Problems in Existing Communication Infrastructures
(A-1) Technologies and Problems in Ground-base Communication Infrastructures
In a case where large-sized data, like image files, are transferred from the movable bodies like automobile to a ground-base fixed station, communication methods via ground-base communication infrastructures or communication satellites can be considered. However, existing communication methods may not satisfy all the requirements for the system specification and performance.
Now, let's take as an example an ambulance. For carrying an emergency case by ambulance, the average carrying time period is about 27 minutes. For serious cases, there occurs many instances in which the emergency case may die if adequate medical treatment is not applied in time, which is a strong motivation for the medical specialist to apply medical treatment to the emergency case in the ambulance or to suggest an adequate method for medical treatment to the emergency case to the emergency medical technician in the ambulance. However, about 15,000 or more medical doctors would be required for paramedic services in order to dispatch medical doctors with shift work to the about 5,000 ambulances in Japan. However, this is not realistic, and so it is considered to be more effective to communicate adequate methods for medical treatment from the paramedic center to the ambulance. However, in the conventional ground-base communication systems, communication lines with phone-level quality with which an instantaneous break may occur frequently are only available, and therefore, adequate methods for the medical treatment can not be directed satisfactorily from the paramedic center. If image information captured by endoscope, electrocardiogram, echo and camera could be directly transferred to the paramedic center, it is supposed that satisfactory diagnosis and directions for medical treatment of the emergency case could be given. However, ground-base communication infrastructures have such problems as limitation of transmission band, limitation of communication coverage areas, cross talk and interference due to reflection by man-made building structures, and so can not be applied to practical use for such a purpose.
Similarly, though many requests exist for large-scale data transmission from movable bodies, for example, live telecast of a marathon, the conventional ground-base communication infrastructure can not be used for this application.
(A-2) Technologies and Problems in a Geostationary Communication Satellite System
In the field of satellite communications using artificial satellites, communication systems using geostationary satellites and low-to-middle altitude orbits are well known. There are the following problems in conventional communication satellites.
As a geostationary satellite has about a 24-hour orbit cycle almost equal to the earth's rotation cycle, the geostationary satellite can be viewed from the ground to be stationary at a point above the Equator. However, the elevation angle of such a geostationary satellite is low, for example, the elevation angle at Tokyo is at most 45 degrees even in case of good conditions. As the movable bodies in metropolitan areas move on the roads surrounded by artificial building structures and roadside trees, the lower range of the elevation angle is blocked by those obstacles, and satellite communications with geostationary satellites may be blocked. As the stationary satellites can be seen in an east-south to west-south direction, though communication lines can be established in a case where the movable body moves in a north-to-south direction and a broader visual field to the satellite can be obtained, communication lines may be blocked by building structures and roadside trees at almost any time in a day in a case where the movable body moves in an east-to-west direction, especially, in a west direction. Therefore, satellite communications using geostationary satellites do not produce satisfactory results for service in not-plain areas, like a metropolitan area and a mountain area.
(B) Technologies and Problems of Satellite Communication Systems Currently under R&D
In the case of satellite communication systems using low-to-middle altitude orbits, such as Iridium and Odyssey currently under development for the purpose of cellular phone services using mobile communication satellites, the duration of time while the satellite in service stays within a high elevation angle range and comes in sight from the ground is generally short due to the limitation on the number of orbital planes for the satellite and the number of satellites in service. Especially, since a satellite flying on the low altitude orbit has about 90 to 100 minutes in its orbit cycle, the duration of time while the satellite stays within a high elevation angle range as viewed from the ground is as short as a few minutes. Therefore, when trying to use or apply this kind of satellite communication systems for the purpose of stable and definite communication for large-scale data, as used in the above example of an ambulance and a paramedic service system, without any influence by building structures, plants and natural topographic features over a certain extended time period, for example, more than 27 minutes, it is required to configure such a system using plural satellites which alternately may come in sight at a higher elevation angle. In this case, some thousand or more satellites are required, which causes difficulties in procuring a number of satellites, the operation thereof and launching cost reduction, and so this plan is not practical also from an economical point of view.
In the case where a higher elevation angle is required, as in the above example, conventional geostationary satellites for practical use and low-to-middle altitude satellites currently under development are not fully applicable.
(C) Technologies and Problems in a Satellite Communication System Currently under Study
For example, as found in research reports, such as “Feasibility of Mobile Communication Mission Using NonGeostationary Satellite Orbits”, Technical Research Report, Japanese Electronics, Information and Communication Society, Vol. 89, No.57, satellite communication systems currently understudy are discussed. Especially, an oblong orbit having a larger eccentricity squared is proposed in some research reports including the above report.
According to Kepler's Law, an object passing around the apogee point of the orbit slows down. By defining an orbit having its apogee point located on the
Hamano Nobuo
Ikeda Masahiko
Ito Masahiro
Maeda Toshihide
Nakamura Shigeki
Antonelli Terry Stout & Kraus LLP
Eldred J. Woodrow
Hitachi , Ltd.
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